Suppose a ball has a potential energy of 5 J when you drop it. What would be its kinetic energy just as it hit the ground? (Ignore the effect of air resistance.)
If you simply drop it ... so that it's not moving until you let it go ... then the kinetic energy it has when it hits the ground is exactly the potential energy it had while you were holding it.
5 J potential energy in your hand ===> 5 J kinetic energy when it lands
